i having trouble with my iPod

i just got a prepaid card and i went online to download some songs for my iPod mini and i did i download all the songs i want that i can get and one day i went to get my iPod then i can listen to the songs but all the songs off of my iPod is gone the songs is not even om my computer and i want to know how to get all songs back

I have a problem i download some songs off of my prepaid card didn't want and i want to know if i can erase the songs and get the money back on my prepaid card then i download some more songs

so if anyone know how to fix this can you email me at lindseycone@yahoo.com

Please

Thanks